Effect of different metal primers and opaquers on shear bond strength between titanium alloy and indirect laboratory composites

Indirect light-cured composite resins have been extensively used in tooth restoration because they can provide acceptable aesthetics, wear resistance similar to tooth structure, and are easy to manipulate in the laboratory and to repair. However, durable bonding between composite resins and metal frameworks has been challenge. Macro or micro mechanical retention on the metal substructures such as beads, loops and pits, or sandblasting and etching, were the only mechanisms for bonding composite materials to metallic substrates. However, recent developments resulting in chemical bonding have been achieved, including silicoating systems and functional monomers systems. Controversial and limited studies concerning adhesive performance between indirect composite and titanium alloys has led to the lack of an informed design rationale for bonding composite materials to titanium alloys. The current study evaluated the effect of different metal primers and opaquers on the bond strength between titanium alloy (Ti6Al4V) and indirect laboratory composites. For the present study, 4 diffent indirect composite systems and 380 Ti6Al4V samples were used. Groups were created by metal primer brands and divided into 4 main groups; Group 1 (GC, Metal Primer II) was consisted of 80, Group 2 (Shofu, ML Link) was consisted of 100, Group 3 (Ivoclar Vivadent, SR Link) was consisted of 100, Group 4 (Bisco, Z-Prime) was consisted of 100 samples. 10 mm diameter and 5 mm thickness Ti_6 Al_4 V alloy samples (as machined) were sandblasted with 50 μm Al2O3 particles. Group 1 was consisted of 8 subgroups and Group 2, 3 and 4 were consisted of 10 subgroups, totally there were 38 subgroups each have 10 samples. After sample preparations, thermal cycle application was performed to only 19 subgroups before testing and the remaining 19 subgroups were directly tested after by a shear bond strength machine with a 1 mm/min crosshead speed was used. Mean shear bond strengths and standard deviations were calculated. Statistical analysis of the data for all groups was accomplished by one-way ANOVA. Shear bond strengths differences between different groups were evaluated with two-way ANOVA. Multiple comparisons were made with Tukey's HSD test and Student t-test was used for the comparision of parameters between two groups. As a result, when evaluating the 38 test groups, the group which was prepared by Bisco Z Prime as metal primer, GC Gradia as opaquer, GC Gradia as indirect composite resin and thermal cycle procedure were applied showed the highest (Group 4.3a: 13.74 ± 2,09 MPa) value and the group which was prepared by Ivoclar SR Link as metal primer, Bisco Tescera as opaquer, GC Gradia as indirect composite resin and thermal cycle procedure were applied showed the lowest (Grup 3.3a: 3,29 ± 0,52 MPa) value. There was no significant difference between shear bond strengths of metal primer groups (p>0.05). There was significant differences between shear bond strengths of opaquer groups (p<0.01). Between all groups when evaluated by thermal cycle application, the mean shear bond strength of thermal cycle applied groups were significantly lower then the non-applied groups (p<0.05). Common factor of opaquer and metal primer was effected the shear bond strengths significantly (p<0.01). Common factor of opaquer and thermal cycle was effected the shear bond strengths significantly (p<0.01). Common factor of metal primer and thermal cycle was effected the shear bond strengths significantly (p<0.01). Common factor of opaquer, metal primer and thermal cycle was effected the shear bond strengths significantly (p<0.01). In all 380 debonded surfaces, combined failures was detected on 232 samples, adhesive failures was detected on 148 samples. None of the surface showed cohesive failure. In the present study, the used indirect composite systems have different chemical composition, application procedures and polymerization durations. Within the limitations of this experiment, different but chemically appropriate metal primers, opaquers and indirect composite resins, together can be used for preparing or repairing indirect composite restorations as a superstructure for Ti6Al4V.